The present invention relates to a transmission power controller and a transmission power control method capable of carrying out stable transmission power control independently of the number of the channels to be multiplexed by a modulator in the transmission power control in a CDMA communications system.
FIG. 5 is a block diagram showing a configuration of a conventional transmission power controller. In FIG. 5, the reference numeral 1 designates a modulator for carrying out spreading and modulation and multiplexing of a plurality of user communication signals CH1-CHn fed from a baseband stage (not shown) in order to spread the spectrum of each narrow band user communication signal to a wide band signal. The communications system is referred to as a CDMA (code division multiple access) system. The reference numeral 2 designates a mixer for mixing a transmitted signal output from the modulator 1 with a signal output from a local oscillator 3; 4 designates a variable attenuator for carrying out attenuation control of the transmitted signal passing through the mixing by the mixer 2 in response to an attenuation control signal slot by slot, for example; 5 designates a power amplifier for amplifying the transmitted signal passing through the attenuation control by the variable attenuator 4 to be output.
The reference numeral 6 designates a detector for capturing the amplified transmitted signal via a coupler 6a at every predetermined time interval, and for detecting it. The reference numeral 7 designates an A/D converter for A/D converting the transmitted signal captured by the detector 6; 8 designates a comparator for comparing the output signal of the A/D converter 7 with a reference signal captured by a reference voltage generator 9, and for outputting the compared result; 9 designates the reference voltage generator for generating the reference voltage from the total transmission power of the user communication signals multiplexed by the modulator 1; and 10 designates a compared result output section for supplying the variable attenuator 4 with the compared result output from the comparator 8.
Next, the operation will be described.
First, the modulator 1 carries out the spreading and modulation of the plurality of user communication signals CH1-CHn fed from the baseband stage, and multiplexes the spread modulated signals. Then, the mixer 2 mixes the transmitted signal supplied from the modulator 1 with the signal supplied from the local oscillator 3, and outputs the mixed signal. Subsequently, the variable attenuator 4 carries out the attenuation control of the transmitted signal passing through the mixing by the mixer 2 in response to the attenuation control signal supplied from the compared result output section 10 slot by slot, for example. The transmitted signal undergone the attenuation control is amplified by the power amplifier 5 to prescribed transmission power, and is radiated from an antenna not shown.
The attenuation control signal is produced by the compared result output section 10 which is supplied with the compared result from the comparator 8 that compares the reference signal generated by the reference voltage generator 9 from the total transmission power information fed from the modulator 1 with a detected voltage signal produced by the detector 6 that detects the transmitted signal it captures via the coupler 6a. 
The feedback control of the transmission power signal thus carried out makes it possible to generate a stable transmission power signal independently of aging or variation in the power amplifier 5 or its peripheral components.
In such a conventional automatic power controller (APC), however, the voltage amplitude of the transmitted signal output from the power amplifier 5 varies greatly in accordance with the number of channels to be multiplexed by the modulator 1, thereby resulting in large variations in the detected output signal of the detector 6 even for transmission signals equal in power. Thus, although the modulator 1 produces the transmission power signal equal in power, the actual transmission power stabilized by the APC control varies in response to the number of channels to be multiplexed.
With the foregoing configuration, the conventional transmission power controller has a problem of being unable to carry out accurate power control of the transmitted signal because of the large fluctuations in the detected output signal of the detector 6 in response to the number of channels to be multiplexed by the modulator 1.
The present invention is implemented to solve the foregoing problem. It is therefore an object of the present invention to provide a transmission power controller and a transmission power control method capable of achieving highly accurate transmission power control independently of the number of channels to be multiplexed by the modulator.
According to one aspect of the present invention, there is provided a transmission power controller comprising feedback means for generating an attenuation control signal by comparing a detected output processed signal with a reference signal, the detected output processed signal being produced as a result of the root-mean-square processing of a detected output signal of a transmitted signal captured by detecting means.
This offers an advantage of being able to achieve stable transmission power control independently of the number of channels to be multiplexed by a modulator.
According to another aspect of the present invention, the feedback means can carry out a plurality of times the root-mean-square processing of the detected output signal of the transmitted signal captured by the detecting means, carry out moving average processing of the signal undergone the root-mean-square processing, and generate the attenuation control signal by comparing the signal passing through the moving average processing with the reference signal.
This offers an advantage of being able to achieve stable transmission power control independently of the number of channels to be multiplexed by a modulator.
According to a still another aspect of the present invention, there is provided a transmission power control method of a transmission power controller comprising the step of generating an attenuation control signal by comparing a detected output processed signal with a reference signal, the detected output processed signal being produced as a result of the root-mean-square processing of a detected output signal of a transmitted signal.
This offers an advantage of being able to achieve stable transmission power control independently of the number of channels to be multiplexed by a modulator.
According to anther aspect of the present invention, the transmission power control method of the transmission power controller can carry out the root-mean-square processing of the detected output signal of the transmitted signal, carry out moving average processing of the signal undergone the root-mean-square processing, and generate the attenuation control signal by comparing the signal passing through the moving average processing with the reference signal.
This offers an advantage of being able to achieve stable transmission power control independently of the number of channels to be multiplexed by a modulator.